Skin friction measurement and drag reduction of porous media under cryogenic and high Reynolds number conditions

To investigate the drag reduction laws and the Reynolds number effects of porous media under cryogenic and high Reynolds number conditions, this study conducted skin-friction measurements and drag reduction experiments in a 0.3 m transonic cryogenic wind tunnel. Pressure sensors and oil flow devices were installed downstream of the smooth plate and porous media region respectively, to measure the power spectra of fluctuating pressure and the global skin friction. It is shown that the skin friction coefficient decreases with the increase of Reynolds number. With the increase of Reynolds number (increasing the Mach number or decreasing the total temperature of the incoming flow), the porous media drag reduction ratio shows a non-uniform decreasing trend. Besides, the introduction of porous media, the low-frequency signal strength of the downstream pulsating pressure increases, and the intensity of the high-frequency signal is weakened. Under the typical condition that Mach number Ma = 0.300, Reynolds number Re = 7.51×10⁶ and the total temperature of the incoming flow T₀ = 140 K, the drag reduction ratio of porous media is 11.4%, which initially verifies the feasibility of the drag reduction control strategy under low temperature and high Reynolds number conditions.